Requirements for a global lidar system: spaceborne lidar with wall-to-wall coverage

Hancock, Steven; McGrath, Ciara; Lowe, Christopher; Davenport, I. J.; Woodhouse, Iain

doi:10.1098/rsos.211166

Cited by 33 publications

(22 citation statements)

References 53 publications

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“…The swath width of a spaceborne lidar can be calculated by considering the lidar performance and the spacecraft orbital velocity. The lidar equation can be combined with the orbital velocity equation to express the swath width as a function of orbit altitude as [18] where s is the swath width, P pay is the power available to the lidar payload from the spacecraft bus, L e is the laser efficiency, E det is the energy detected at the receiver (after detector efficiency losses), A is the telescope collecting area, h is the orbit altitude, is the atmospheric transmittance, Q is the detector quantum efficiency, is the surface reflectance, R is the mean Earth radius, r is the desired spatial resolution of the instrument, and is the standard gravitational parameter of Earth. A full derivation of equation ( 1) is provided in [18].…”

Section: Swath Widthmentioning

confidence: 99%

“…To avoid this, a minimum resolution limit ( r min ) is defined that will ensure that a continuous track at least one pixel wide with E det per shot can be produced. This is detailed in [18] and can be calculated by using equation (1) and letting s = r = r min , giving (4)…”

Section: Resolutionmentioning

confidence: 99%

“…Assuming that full coverage of the largest latitude band will ensure full coverage of all visible latitude bands, the minimum number of spacecraft required to provide the desired coverage in a given time can be calculated as where f cloud is the assumed global mean cloud fraction, such that 0 ≤ f cloud ≤ 1 . It should be noted that this is an approximation of the impact of cloud cover, and more precise calculations of the probability, as in [18], could be used without impacting the presented approach. The total time to desired coverage in seconds is t, and T is the satellite orbit period, calculated for circular orbits as ( 7)…”

Section: Number Of Spacecraftmentioning

confidence: 99%

“…The propellant mass ( M p ) required to maintain a specific orbit for a lifetime duration of L can be calculated as where I sp is the specific impulse of the propulsion system being used and g 0 is the acceleration due to gravity (at sea level), taken as 9.81 m∕s 2 . Combining equations ( 15) - (18), the mass of propellant required to maintain the orbit altitude can be written as a function of altitude, as ( 15)…”

Section: Propulsion Backgroundmentioning

confidence: 99%

“…VLEO is a potentially advantageous regime for spaceborne lidar desiring high, or even global, coverage. At lower altitudes, the energy that must be emitted by the lidar to achieve sufficient detected energy at the receiver, is reduced [18]. A lidar instrument designed for operation at lower altitudes can hence achieve the same spatial resolution as those at higher altitudes, while allowing the laser power to be spread over a wider swath.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of very low Earth orbits (VLEOs) for global spaceborne lidar

et al. 2022

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Very low Earth orbits (VLEOs) have been proposed as a beneficial space mission regime due to their propensity to increase instrument spatial resolution and reduce launch cost per unit mass. However, for visual instruments, these benefits come at the cost of a decreased instrument swath width. This reduction results in longer revisit periods for regions on Earth and longer time until global coverage is achieved. Conversely, light detection and ranging (lidar) as an active remote sensing technique, can benefit from larger swath widths at lower altitudes, due to the increased signal-to-noise ratio. Investigation of this relationship shows that lidar swath width is inversely proportional to altitude squared, and, as a result, the number of spacecraft required to provide a desired lidar coverage also decreases approximately in inverse proportion to altitude squared. Investigation of suitable propulsion systems shows that although propellant mass and number of thrusters required for orbit maintenance increases with decreasing altitude, the overall system mass, and hence launch cost, will, in general, tend to decrease with decreasing altitude due to the lower number of spacecraft required. For a given mission, spacecraft bus, and propulsion system, a VLEO altitude can be identified that will result in the minimum overall mission cost.

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Section: Swath Widthmentioning

confidence: 99%

Section: Resolutionmentioning

confidence: 99%

Section: Number Of Spacecraftmentioning

confidence: 99%

Section: Propulsion Backgroundmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Investigation of very low Earth orbits (VLEOs) for global spaceborne lidar

et al. 2022

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Comparison of three global canopy height maps and their applicability to biodiversity modeling: Accuracy issues revealed

Moudrý,

Gábor,

Marselis

et al. 2024

Ecosphere

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Global mapping of forest height is an extremely important task for estimating habitat quality and modeling biodiversity. Recently, three global canopy height maps have been released, the global forest canopy height map (GFCH), the high‐resolution canopy height model of the Earth (HRCH), and the global map of tree canopy height (GMTCH). Here, we assessed their accuracy and usability for biodiversity modeling. We examined their accuracy by comparing them with the reference canopy height models derived from airborne laser scanning (ALS). Our results show considerable differences between the evaluated maps. The root mean square error ranged between 10 and 18 m for GFCH, 9–11 m for HRCH, and 10–17 m for GMTCH, respectively. GFCH and GMTCH consistently underestimated the height of all canopies regardless of their height, while HRCH tended to overestimate the height of low canopies and underestimate tall canopies. Biodiversity models using predicted global canopy height maps as input data are sufficient for estimating simple relationships between species occurrence and canopy height, but their use leads to a considerable decrease in the discrimination ability of the models and to mischaracterization of species niches where derived indices (e.g., canopy height heterogeneity) are concerned. We showed that canopy height heterogeneity is considerably underestimated in the evaluated global canopy height maps. We urge that for temperate areas rich in ALS data, activities should concentrate on harmonizing ALS canopy height maps rather than relying on modeled global products.

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Spaceborne LiDAR for characterizing forest structure across scales in the European Alps

Mandl

Stritih

Seidl

et al. 2023

Remote Sens Ecol Conserv

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The launch of NASA's Global Ecosystem Dynamics Investigation (GEDI) mission in 2018 opens new opportunities to quantitatively describe forest ecosystems across large scales. While GEDI's height‐related metrics have already been extensively evaluated, the utility of GEDI for assessing the full spectrum of structural variability—particularly in topographically complex terrain—remains incompletely understood. Here, we quantified GEDI's potential to estimate forest structure in mountain landscapes at the plot and landscape level, with a focus on variables of high relevance in ecological applications. We compared five GEDI metrics including relative height percentiles, plant area index, cover and understory cover to airborne laser scanning (ALS) data in two contrasting mountain landscapes in the European Alps. At the plot level, we investigated the impact of leaf phenology and topography on GEDI's accuracy. At the landscape‐scale, we evaluated the ability of GEDIs sample‐based approach to characterize complex mountain landscapes by comparing it to wall‐to‐wall ALS estimates and evaluated the capacity of GEDI to quantify important indicators of ecosystem functions and services (i.e., avalanche protection, habitat provision, carbon storage). Our results revealed only weak to moderate agreement between GEDI and ALS at the plot level (R2 from 0.03 to 0.61), with GEDI uncertainties increasing with slope. At the landscape‐level, however, the agreement between GEDI and ALS was generally high, with R2 values ranging between 0.51 and 0.79. Both GEDI and ALS agreed in identifying areas of high avalanche protection, habitat provision, and carbon storage, highlighting the potential of GEDI for landscape‐scale analyses in the context of ecosystem dynamics and management.

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Requirements for a global lidar system: spaceborne lidar with wall-to-wall coverage

Cited by 33 publications

References 53 publications

Investigation of very low Earth orbits (VLEOs) for global spaceborne lidar

Investigation of very low Earth orbits (VLEOs) for global spaceborne lidar

Comparison of three global canopy height maps and their applicability to biodiversity modeling: Accuracy issues revealed

Spaceborne LiDAR for characterizing forest structure across scales in the European Alps

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